When fork() fails, clean up data structures.

There are a number of different conditions that could cause
ActivityManager to fail to fork() a process.  One of the most common
ones is a package being "frozen" during a PackageManager operation.

When this happens, use the common forceStopPackageLocked() method
to cleanup any internal bookkeeping structures.  (It's slightly
misnamed, since it doesn't actually "force stop" the app.)  It's
also the same method that we called moments earlier when the package
was first frozen through KILL_APPLICATION_MSG.

Bug: 28395549
Change-Id: I7b1623c5f66fc1de24cad5360c977ea764d09244